<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<style>
   .one{
    color:red;
    font-size:24px;
   }
   .two{
    color:blue;
    font-size:36px;
   }
   .three{
    color:green;
    font-size:48px;
   }
</style>
<title>Insert title here</title>
</head>
<body>
<h2 class="one">选择器one</h2>
<p>正文内容1</p>
<h2 class="two">选择器two</h2>
<p>正文内容2</p>
<h2 class="three">选择器three</h2>
<p>正文内容3</p>
</body>
</html>